Stencil printing apparatus



May 5, 1953 Filed April 19 1951 J. B. THOMAS STENCIL PRINTING APPARATUSfT III-1.

4 Sheets-Sheet l INVENTOR.

JOHN B. THOMAS ATTORNEY May 5, 1953 J. B. THOMAS 2,637,269

STENCIL PRINTING APPARATUS Filed April 19, 1951 4 Sheets-Sheet 2SOLENOID 827 I :11 BRAKE '44 1% 5 e 1 I I2. E

IN VEN TOR.

JOHN B. THOMAS ATTORNEY May 5, 1953 J. B. THOMAS 2,637,269

STENCIL PRINTING APPARATUS Filed April 19, 1951 4 Sheets-Sheet 5 GTIT A.7.7. v.

INVENTOR.

JOHN B. THOMAS F1115. @WWL ATTORNEY May 5, 1953 J. B. THOMAS STENCILPRINTING APPARATUS Filed April 19', 1951 4 Sheets-Sheet 4 INVEN TOR.JOHN B. THOMAS Patentecl May 5, 1953 37,26 STENGEJ mtns rING "APPARATUS:Joh B- lh mas, Wat rwwn, Conn assignor t o B tsan s t?- K s s? creenPrinter, 1nd,; Nevv York, fof New Yer-l;

Application April lii, 1951, 'S erialiNo. 221;794

claim .1

This invention relates :to an apparatus ifpr printing sheets, such astextile fabric webshplasic films and paper, with the aid vof 3a stencil.Roisimplicity, such apparatus will be referred vt hereinafter simply asa silk screen printin ma,- chine, it being" understood that this term,merc 1y is a trade designation for a stencil .prinjging machine and.does not indicate that the =,st;enc il necessarily is of silk.

It is an object of the invention :to provide a power driven silkscreenprinting machine in which a scraper rapidly moving back and forth acrossthe screen reverses and .stODS smoothly and quietly,

More specifically, it is anobjectyof the .in lenr tion to provideamachine of the character de scribed in which the scraper issloyvedldownpr or to reversal .or stopping joy the vprovision of a variable speedtransmission in the 1liinen atic drive tier the scraper and i rsha plr'cre sing the speed redu tion ju t z bsit le th is i' r.= "'r verses 01'stops.

.Iti an her objec of 11 inv nt on is mr ie n apparatu o th ichsra teQessrb din iwh qh ad u t ent ih A ssih-si tmls ef ill 'sq er can be madeeasily and rapidly.

lit another object of the invention ;to provise smas 9 th finan ier 'iescr. .fed wa employs far ewer par son the t top than -:a

r s n d newe .QIAYER s k se pr n in i is s o e pbi s o th nven ion trovide and apparatus of the character qescigibe d in which eith r the Pn 9 s q sins Q? a s sa s :th sc ap ca b ad usted at w ll qe s m t a Web.o an W- posit n.

v; is an ther ob ec e t nven n 1 9 pmi a p ra us o the haracte i d sc ied which i q ash s n trus s tha th 9 r v is aut atica l c t out a an :Pi X 9 scr en t ave i u ama in the a paratus,-

i th l t r onn t pn i is a no; object of the invention to provide an a pH o .t r ha ast r e cribed in whi h the so ans er d ve sautsmst al y utpu i il, s9??? we is raisedso iha thereis no dan er pf hav ng-313sscreen torn.

:I is anoth o ec .9 th inven io 4 movies an ap aratu o the chara te .sisq ibsd -WhiQh is of ruseeq ans durab qon t q i nt er Qbi t th n ent qn il impa be ob u and vm p r w l he oin ed .q j new mafter.

[The invention accordingly cons; ts in the jeatures 0f construction,Combinatio of elements and arrangements of parts which vvill bex'inbiisdin e machine herein s s be n o which i11 co .of appli ion w llb ndic t d n th ppende c imsin t e sqwmp ny ns draw gs, in whic s shownens o the v r-1 1 s p ss b mbodiments o 1th inven on,

z s- 1161 a t p plan i o a p wer driven si k sc een printin mach neconstructed in a corglance with the present invention and having 1 many:dfitails thatare-shown elsewhere o nitteid i s ider to pre ent ontuion;

Fig. 2 is an enlarged fragmentary view taken substantially along theline of ;2?2 of Fig. ane s il ustr t p -th in mati d i e o the Fig. 2ais a schematic gliag-rarn of a hydraulic tra smission unitin i -k nsmatid vs; l

s- 3 1 a sect o a iew taken su sta tial y lon th 1 1? 3-173 Fi A Fist is an -.en re d v asm i y y sw tak along the line 4-.-.-& of Fig. 1and-is illustrative of e mechanisms :iQ stamina and starting the scraperupon rise and fall of the stencil screen; Fig. .-5 i a se tiona .viewtaken al n th 'rl n O :5 of :Fi Fig. 6 is a sectional view takensubstantially a on t n *,6' i F Br n 7 -;is a wiring .vdiagrarn of thecircuit for the-scraper controlmechanism.

in general, the various objects ,of the present invention are achievedby providing a sill; screen printing gnachine in which thescrape'r isactu' ategl from an electric motor throng ha hydraulic t a smissi n- Aemb i i c ud d w i h duplicat s in m n tu e sh move ent .o e scraper andavloich ,fn nc tions as a ,control f or ieysrs ns s pin the ele t m toTh hydraulic ltra smi'ssion enabl s the sc e to be rapiqlr a ce er teand cs e t mmed ately beiorc and after reve sa 1 opp e crime scrape husther i p'rovid.ed Iar we r v for t e scrane which i bothefi c en an quieand which can be adjusted rapidly and with ease. Referr n n w in detaflt t drawi s, the refer-s i nu a memes k screen b riti g m hinsem dy nthe i v ntion a comprising a suitable printing table 1.2 to either sideio'f which a'si ppl y or a take-i 1 reel .(not show disp0se iheip in ibl nins zdes an st apronQM and a reaiiapron l6 s itahly interconnectedby struts (not shown).

A ached t t rea a r n a e .a p ir o spscedfcs iriss J (sesFissand 12 "ia i wall vof e a chof which aligned horizontal axles 20 are journaled.Each of said axles has a-ffixed to it a sprocket 22 about which a chain24 is trained. Moreover, each axle 22 turns a second sprocket 26 aboutwhich a chain 28 is trained. The two chains 28 engage sprockets 30 whichare secured to aligned horizontal axles 32 journaled in the casingsabove the axles 22. Turning with each axle 32 is another sprocket 34.Each sprocket 35 engages a different chain 36 having an upper flight 38and a lower flight 39. Said flights extend forwardly through openings42, M in the front wall of each casing l8. A pair of hollow tubularrails 46, 48 are attached to the front wall of each casingin line withthe openings 42, 44, said rails serving to enclose the flights of thechains 36. At the forward end of each said pair of rails there is fixeda housing 50 in which there is contained an idler sprocket (not shown)about which the associated chain 36 is trained. The housings 56 areconnected by a cross bar 52 which serves to tie together the scrapersupporting frame elements on opposite sides of the machine.

The machine H3 includes a scraper 54 of suitable construction designedto ride back and forth across a stencil screen and to clear the pool ofink at both ends of its travel. One satisfactory form of scraper is thatshown in the co-pending application of John B. Thomas and Courtney E.Moorhouse, Serial No. 726,504

for Stencil Printing Apparatus, filed February 9 5,1947; anotheracceptable form of scraper is the one shown in co-pending applicationSerial No. 221,793 for Stencil Printing Apparatus filed simultaneouslywith the present application, both said applications being assigned tothe assignee of the present application.

Essentially, the scraper includes a blade 55 whose opposite ends aremounted on carriages 58 having wheels 60, 62 located between and ridingon the rails 46, 48 at opposite sides of the machine. Each carriage issecured by a fitting 6 3 to the upper flight 38 of its associated chain36 so that as the chains move back and forth the scraper will be movedin like fashion. The fitting 6 3 rides in a slot 66 at the bottom of theupper rail 56. The machine I0 includes a conventional stencil screen 68secured to a rectangular screen frame 70. The frame is supported betweena front bar 72 and a rear bar 74, the mechanisms used to connect theframe and bars being of any suitable construction and desirably beingsuch as shown, described and claimed in co-pending' application SerialNo. 726,504 for permitting fine adjustments of the position of theframe. Heretofore, only the front support for a stencil screen framecustomarily has been adjustable to accommodate frames of difierentlengths in a direction from front to back of the machine. However, inaccordance with the present invention, both bars 12, 14 are adjustablefor movement toward and away from the front and back of the machine.Thus, the bar M carries at itsopposite ends a pair of brackets 76including clamp portions which are adapted to grip the lower rails 48 onopposite sides of the scraper. The clamp portions are operated by nuts78 so that the rear bar 12 can be adjustably set at any point along thelower rails. The front bar 72 is similarly equipped with clamp portionsso that it too can have its position varied as desired. 7

To supply the power for reciprocating the scraper, each chain 24 istrained about a sprocket .80 fixed to acountershaft 82 located at the 1the pump, thereby forming a closed rear of the machine beneath thetable. Said countershaft spans the distance between the two sets ofrails 46, 48 and carries two sprockets 80, one for driving each set ofchains 24. Secured to the countershaft 82 is a sprocket 84 which isengaged by a chain 86 that is turned by a sprocket 88. Y

In accordance with a principal feature of the instant invention, thesprocket 88 is mounted on the output shaft 90 of a hydraulictransmission unit 92, i. e. a hydraulic unit capable of effecting speedconversion. Said unit includes in its output section a fluid motor M(Fig. 2a) of any conventional type, such far example, as that shown inLesson 47 of the manual entitled the Hydraulics, published by the HenryFord Trade School of Dearborn, Michigan, bearing copyright 1941 andreprinted This type of motor consists of two gears similar to anordinary gear pump. But, unlike an ordinary gear pump, the body of themotor has a pair of passageways leading from the exhaust port to portsdiametrically opposite the exhaust port. The body also has another pairof passageways leading from the inlet port to ports diametricallyopposite to the inlet port.

This type of fluid .motor will deliver rotaryv power in either directionof rotation at all speeds within its rated limits. The motor is capableof extremely rapid acceleration and deceleration, and can be started,stopped, and even stalled repeatedly without damage.

The input section of the unit 92 constitutes a variable delivery pump P,such for example, that shown at Lesson 15 of said manual, the same beinga piston type pump with a stroke which is varied by a change ininclination of a wobble plate. Said pump, when turned at a uniformspeed, is capable of varying its delivery I in accordance with theposition of a controlmember which regulates the inclination of saidplate. The delivery of the pump is connected to the intake of the fluidmotor, and the outlet of the fluid motor is connected to the inlet ofhydraulic circuit (see Fig. 2a).

The pump is driven by a sheave 94 on the input shaft 96 of the hydraulictransmission unit, and the delivery of the pump is regulated by acontrol member 98 secured to a shaft Hi0, whose angular positiondetermines the inclination of the wobble plate and thereby the rate ofdelivery of the pump.

The control member is biased in a counterclockwise direction, as viewedin Fig. 2, by a tension spring I02. When this member is in its extremecounter-clockwise position, as viewed in said figure, the wobble plateis positioned to obtain a maximum piston stroke and, hence, maximumdelivery of the hydraulic fluid. Moving the control member against thespring I02 in a clockwise direction, as viewed in Fig. 2, lessens thedelivery of the pump and consequently reduces the speed of rotation ofthe hydraulic motor M. Due to the extremely rapid response of this typeof motor to fluctuations in the rate of delivery of hydraulic fluid toit," the output speed of the hydraulic transmission unit followssubstantially instantaneously any variation in position of the controlmember 98.

A belt I04 trained around the sheave 94 is driven by a pulley I06. Saidpulley is turned by an electric motor I08 through a fluid clutch H0 ofany suitable type that will permit the motor 103 to be reversed rapidly,or to assume rapidly a -.load. wi hout stalli burnin out the motor,rimnosine an 11 15111 5 h h sur o current inwth im t supnl A m r yclutchis suitable for this purpose.

The countershaft 82 fixedly carries a rnale threaded sleeve H2 whichmeshes with a tapped collar I-I I, so that said collar will duplicateinmini-aturethemotion of the scraper. It will be observed that, murder forthe movement of the collar tohe a faithful reproduction. of the scrapermovement, the kinematic train between the counter-shaft .82 andthecppositeends of the scrapershouldentirely constitute positive(nonslipping) motion-transmitting mechanismasuch, forexamplaas thechainsand sprockets as, 243, 22,125.23, 3.0, 34,3cheretofore described.Moreover,=in orderthat the scraper be capable of as rapidanacceleration,deceleration and reversal as the .hydraulic motor M, apositive motion transmitting mechanism, such as the chain 89and-sprockets 84,188,,is employedto connect the output of the hydraulictransmission'unitto the countershaft. Since slight variations intheirate at which the hydraulic pump P is driven will not noticeablyaffect the operation of the machine, the drive from the clutch IIU tothe hy draulic transmission unit can be effected by sheaves and a belt.This latter connection, moreovenhas the advantage of easing the load onthemotor and power; supply at times 0f reversal :and suddenacceleration.

The collar IIAis secured to a yoke lit having a pair of depending armsH8, I so located on opposite sides of the regulating shaft Hill. The armI'lt supports astud iii-2 extending in a direction parallel to the shaft82 and having its h ad facing the opposite arm I23. The is'threadedlyreceived in the arm M8 to permit adjustment thereof and it is held inany adrusted position by a lock nut I-Z l. horizontally aligned with aroller i oarriedby an erect ear I26 on thecontrol member 98.

The otherarm 26 mounts a stud I28 similar tothe-stud I22, but havingitshead facing in theopposite direction. The stud liil cooperates with aroller I39 horizontally aligned therewith andmounted on a pendant ear Ion the control member 98.

.lfrom the foregoing, it willbe apparent that, when either stud contactsits associated roller, the control member 93 will be rotatedinaclockwise direction, as viewed in Fig. 2, t0 decelerate thcoutput' shaft98 of the hydraulic transmission unit. @Moreover, as soon as either studdisene a esit-s associated roller, the control member will be turned acounterclockwise direction, as viewed in Fig. 2, by the tension springI532. Movement of the control member in the latter direction is limitedby abutment of said member against :a vertically adjustable stop M2. Theposition of said stop is-set inaccordance with the speed at which thescraper is desired to traverse the screen 68 during the 'major portiQILof its travel.

Theyoke us also carries an extension its on which there are mounted a"pair of hori zontal threaded studs I35, I 38. These studs, likethestuds I22, I28, are adjustably supported on the yoke. -The studs I36,I38 face inopposite directions and may be disaligned, although theypreferably are parallel. The upper stud Ito is horizontally.alignedwithan actuating element I40 of a momentary electric switch I42. Thisswitchis of the twopole single throw type having one normally Open andone normally closed pair of contacts whioh late-rwill be described'inSaid stud is detail. Th lower t d I 8 5 orizontally a igned with e acuat ng ment I44 of another mo mentary electric switch I46 that likewiseof the two pole single throw type having one normally open and onenormally closed pair of contacts. The switch I42 is the one which isactuated by the stud I38 at the time that the scraper is to be broughtto a stop at-the rear of the machine, and hence, this switch will bereferred to hereinafter as the stop switch. Thev switch 14s is engagedby the stud I38 when the scraper is to be reversed at the front of themachine and hence, said switch will be referred to hereinafter as thereverse switch.

The stop and reverse switches are mounted on a stationary panel I48 andare connected by suitable wiring in a control circuit soon tobedescribed for the electric motor I88.

The yoke H6 is prevented from rotating by a guide spindle hill securedto the stationary base iliI of the hydraulic transmission unit. Saidspindle is slidable in a bore I52 near the tip of the yoke arm I20.

The axles 26 extend from the casings I8 in which they are journaled andsecured in brackets I54 located alongside said casings. Hence, thescraper support, consituting the casings I8, the two pairs of upper andlower rails 46, .48,the housings Eli, and the crossbar 52, pivots aboutthe aligned axles 26 at the rear of the machine, Pivotal movement of thescrapersupport will raise or lower the scraper with respect the printingtable it, and, since the stencil screen also is carried by the sameframe through the medium of the bars 72, 14, will raise and lower thestencil. Thus, the instant machine eliminates the dual supportsheretofore independently employed for mounting the scraper and thestencil.

The lower side of the crossbar 52 is engaged by a follower I56 (seeFigs. 4 and 5) consisting of a roller E53 horizontally journalled on ashaft Hill carried between the arms of a yoke I62. Said yoke is securedon the upper end of a shaftJM slidably mounted for vertical movement in-,a bushing I66 fixed to the front apron I4. The bushing carries a guidebolt I68 having a dog tip I18 slidable in an axial slot Il2 in the shaftI64 to prevent rotation thereof.

The lower end of the shaft fixedlysupports a block I14 having a pin ITS.A similar pin 11.8 is carried by the bushing I65, said pins havingstretched between them a tension spring 180 that biases the shaft I54upwardly.

One side edge of the block I74 is fashioned into a face cam 82 designedto engage a roller actuating element (not shown) of a momentary electricsafety stop switch I84 that is carricdby a post I 85 depending from thefront apron I4, said switch being of the single throw, double pole type,including two pairs of normally closed contacts. The cam I 82 actuatesthe switch I84 when the crossbar 52 is raised from its printing positionshown in Figs. 4 and 5.

The post i86 also mounts a momentary elec-v trio starting switch 583,this being of the single throw, single pole type, but including a pairof normally open contacts. The switch I88 has a roller actuating elementI99 which, in'Fig. 4, conceals the roller actuating element for theswitch I84. The element I98 is operated by a lever Hi2 pivotally mountedby a post I94 on the block I'M. The lever is ecoentrically disposed withrespect to the post It l so that the opera.- tive short end of the leveris biased in a counterclockwise direction, as viewed in Fig. 4. A stopwardly by the roller i964 as the shaft moves up; However, when untilsaid tip clears the roller. the shaft i6 moves downwardly from itsuppermost position, the operative tip of the lever cannot cam past theroller 599 inasmuch as rotation of the lever is prevented by the pin I95so that upon-such downward movement, the lever I62 forces the'ro1ler'I9B toward the switch I68 and closes the normally open contactsthereof.

A suitable electric circuit is provided for operating the motor I68,said circuit being illustrated in Fig. '7. The motor derives electricpower from three-phase cusses I96, I98, 206, only one phase i36-l98 ofwhich is employed for the purpose of controlling the motor.

Normally, the machine is idle, that is, the scraper is at rest at therear of the machine with the upper switching stud I36 engaging theactuating element Hit) in the position of the collar II 15 correspondingto said position of the scraper.

The machine is started by lowering the scraper mount. This causes theshaft I64 to be depressed and the lever I92 to actuate the startingswitch I88. Actuation of said switch is designed to energize thesolenoid 262 of a forward operating motor relay 264 which controls fournormally open sets of contacts 266, I66, 2H], 2I2. The energizingcircuit for the solenoid 262 extends from the bus I96 to the bus I68running through a wire 2H4, the momentarily closed but normally openpair of contacts 256 of the starting switch I68, a wire 2 8, a pair ofnormally open contacts 226 of the stop switch 142 which, however, noware closed because the scraper is at the rear of the machine and thecollar H4, accordingly, is in engagement with the actuating element I 46of said switch, a wire 222, the solenoid 202, a wire 224, a pair ofnormally closed contacts 226 f the reverse switch I46, a wire 228, apair of normally closed contacts 229 of the safety stop switch I84, awire 236, a pair of normally closed contacts 233 of an emergencymomentary stop switch 232 (see also Fig. l) and a wire 233. As soon asthe solenoid 262 is energized, it draws up and closes all the contactsof the relay 264.

Closing the pair of contacts 266 completes a holding or stick circuitfor the forward operating relay 26: 3 as follows: from the bus I96through a wire 23 5, the pair of closed contacts 266, a wire 236, theWire 222, the solenoid 262, the wire 224, the pair of closed contacts226, the wire 228, the pair of closed contacts 229, the wire 238, thepair of closed contacts 23!, and the wire 233 to bus 198, so that whenthe switch I42 is released, the relay 26 5 will remain energized.

Closing the contacts 263, 21c, 2|2 connects the bus I96 to a motorterminal 238 through the wire 234, the pair of closed contacts 268 and awire 246; the bus I 9-8 to a motor terminal 242 through a wire 244, thepair of closed contacts 212. and a. wire 246; and the bus 266 to thirdmotor terminal 246 through a wire 256, the pair of closed contacts 2H3and a wire 252. The connections are such as to turn the motor over in aproper direction to drive the variable delivery fluid pump P in thecorrect sense to rotate the fluid motor M in such fashion that thescraper isdrivjen toward the front of the machine The field 254 of themotor is energized throughout working hours, the conventional con-'nections therefor being omitted to simplify the drawings.

It thus will beseen that as soon as the scraper support is lowered thestarting switch I88 will be closed and the motor I68 will start to movethe scraper from the rear to the front of the machine, the scrapercontinuing to move even after the actuating tip of the lever I92haspassed the roller I and permitted the switch I88 to reopen.

At the time the scraper starts, the roller I36 on the control member 98is engaged by the lower speed control stud I28. Accordingly, the scraperstarts up slowly. But as soon as the scraper has moved a short distanceand the colla-r II4 has experienced a corresponding movement, the studI28 is backed off and the con-- trol member shifted by the spring I62into abutment with the stop I32. As this occurs, the scraper speeds uprapidly, it being observed that the roller I30 is quite close to theshaft I 00' which the control member turns so that after a very shortmovement of the scraper the hydraulic transmission unit is set at itstop adjusted speed.

When the scraper nears the front of the machine, the upper speed controlstud I 22 will contact the roller I26 to slow down the rate of deliveryof the fluid pump P, and thus the rate ofspeed of the hydraulic'motor M,so that very shortly before the scraper reaches the forward limit of itstravel, it is rapidly decelerated. This deceleration does not requireabsorption of the momentum of the scraper and its affiliated parts bybuffers, brakes, or the like mechanical power absorption mechanismswhich create noise and shock. In the present construction the momentumis absorbed by the hydraulic transmission unit, the same beingtransmitted from the scraper to said unit in a positive fashion by thedivers chains and sprockets.

Very shortly after the upper speed control stud I22 has caused thescraper to be slowed down, the lower switching stud I33 engages theactuating element I44 of the reverse switch I46. As this occurs, thepair of contacts 226 of said switch I46 open, deenergizing the holdingcircuit for relay 264 and thereupon terminating rotation of the electricmotor I66 in the direction which causes the scraper to move forwardly.

At the same time, the normally open pair of contacts 256 of the reverseswitch close, thereupon completing a circuit from the bus I96 through awire 256, said pair of closed contacts 256, a wire 266, a wire 262, asolenoid 264 of a reverse operating motor relay 266, a pair of normallyclosed contacts 266 of the stop switch I42, a wire 276, the wire 228,the pair of normally closed contacts 226 of the safety stop switch I84,the wire 236, the normally closed contacts 23I of the emergency stopswitch 232, and the wire 233 to the bus I96 so as to energize the relay266.

The reverse operating relay 266 controls four pair of normally opencontacts 272, 274, 276,

278. The first pair of contacts 272 functions as the holding means forthe reverse relay. When these contacts 272 are closed, a stick circuitis energized for the solenoid 26d. Said circuit extends from the bus I98 through the wire 233, the closed pair of contacts 23I, the wire 236,the closed pair of contacts 229, the wire 228, the wire 270, the closedpair of contacts 268, the solenoid 264, the wire 262, the wire 260, theclosed pair of contacts 272, a wire 280, and the wire'256 to the'busI96.'-

aeamce Closing the contacts .214, 218-1andr218 reverses one phase of:the power supply" to. the threephasemotor Hi8; That'is to say, the bus.200 still? will be connected: to motor: terminal 248,althoughthroughthe.contacts 216 of the reverse operatingsmotor relay,ratherithan' through contactsiZ-IO Of the forward operating motor relay:However, the 'bus. I96, instead of being connected to' motor terminal.238, now. will be connected-to motor terminal 24 2 through contacts" 2"of the: reverse operating motor-"relay; and the bus- I98, instead ofbeing connected: to. motor. terminal 242', now'will be connectedtoxmotor terminal 2'38 througlr contacts 218 of .thereverseoperab in'g'motor: relay. As soon as the direction of travel of. themotorisreversed, thescraperwill startzto moveback toward the'rear. ofthe ma-- chine; and, iniso. doing, first willcause the speedofttheihydraulic' motor, and hence the scraper, to tie-rapidlyaccelerated; thisbeing caused by disengagement ofthestud I22: and roller[26.-

When the scraper nears the rear of. the machine, thespeed thereof is.decelerated rapidly upon-engagement of the-studv l28and the roller I304.Very shortly thereafter the stud I36 will engage the actuating elementI40 ofstop switch M2: to. thereupon open the pair of contacts Z68whichdeenergizes-the stock circuit'for the solonoid 264 sothat the-motorIOS isrendered ineffective.

Thus thescrapcr'willistop at the rear of the machine: If it is: desiredto have the scraper run-through another cycle; a pair of normally opencontacts 281- of a momentary repeating switch282-.are-closed,.thesecontacts being connccted in shunt withthe:contacts 21E so that closure; thereof: will repeat-the cyclehereina-bove described If; at any time; during, a; cycle, the:- railassemebly.- carrying, the. stencil. frame should bev raised, eitheraccidentally or. otherwise, allmotor control circuits fromthe bus: I98.immediately are opened,.so-that the motor lilais stopped; The scraperalso is stopped.

It is desirablefor-the scraper to be brought to a quick stop. so that ifthescreenshould beraised rapidly thescraper will nottear. the same Tothis end I provide a brake 234cm the counter-- shaft 82,saidlbrakebeinga solenoid brake. of any conventional'type,ior'example,one such asshown anddescribedin: detailin application Ser. No. 726,504..Thebrakehas; a pair of shoes which are. designed toengagea drummountedtoturn. withthe coimtershaftn A spring biases theshces intoengagement. with the drumand. a. solenoid 286 (Big; 7 whenenergizedholdsthe shoesapart. Thev solenoid is connected. by a lead wire. 288 to. thebus. 299 andby a-lead wire 285i toazpair. of normally closed contacts2&2.- of the switch I 8.4. Another lead wire 2% runs from said contactsto the. bus L98. Thus as-long. as-theswitch I84: is idle. (the. crossbar5.2 isdown) thesolenoidwill beenergized' andthecountershaft-fi free. Butasisoon. as the, rail assembly carrying the; stencil frame. israisedand. the switch. H84 actuated to stop the motonthe solenoid willbedeenergized permitting; the springto brake the rapidly movingscrapen.

It. thus, willbe. seen that there isprovided. a machine which achievesthe, several objects: of this. invention and is well adapted to meet theconditionsof practical use.

As-various possible. embodiments-might be made of the. abovev invention,and as various changes might. be made in the embodiment. above. set

10' forth, it is to be understood thatall matter. here: indescribed orshown in the accompanying drawings is to be interpreted as illustrativeand not in a limitin sense.

Having thus described the invention, there is claimed as new and desiredto be secured by Letter Patent:

1'. In a silk screen printing machine having a printing table, ascraper, a track guiding said scraper for-movement back and forth acrosssaid table; an element, means to mount said element for reciprocation, apositive kinematic train interconnecting said scraper and said element,said train including a motion reducing mechanism whereby said elementduplicates in miniature the movement of the scraper, a reversibleelectric motor, a hydrauiic speed-varying transmission unit driven bythe electric motor, a control member regulating the'output speed of. theunit, means to drive the scraper from the unit, a control.circuit'forsaid electric motor, a starting switch, and switchesfor-governing theoperation of said motor, said last named switches and said controlmember being so disposed for actuation by said element that uponactuation of said starting switch said scraper Willstart at slow speedfrom the rear of the machine, rapidly accelerate, subsequently rapidlydecelerate as it approaches the front of the machine, reverse at thefront of the machine, slowly start to the rear of the machine, rapidlyaccelerate, subsequently rapidly deceler ate as it approaches therear-of the machine; and finally stop as it reaches the rear of themachine.

2. In a silk screen printing machine having a printing table, a scrapen;a track guiding said scraperfor movementback and forth across saidtable, an element,.means to mount said element for reci cation, apositive kinematic train intel-connecting said scraper and said element,said train including a: motion reducing mechanism whereby id eieznentduplicates iii-miniature the movement of the scraper, a reversibleelectric motor: drivingsaid scraper, switches actuated by said elementfor reversing the motor when the scraper reaches the front of themachine and stoppingthe motor when the scraper reaches the rear of themachine, and a starting switch.

3. In a silk screen printing machine having a printing table, a scraper,a track guiding said scraper-for movement back and'forth across saidtable, .a. reversible electric motor, means governed by theposition ofthescraper to reverse the electriciniotorwhenthescraper reaches thefront-of the ma'chineand to. stop the electric motorwhen the scraperreaches the rear of the machine, means: to start the scrapertoward thefront of the machine from the rear of the machine, ahydraulic:speed-varying transmission unit driven by the electric motor,a control. member regulating the output speed of the unit, meanstodrivethe scraper'from the unit, means governed by-the position of thescraper and actuating the control member so as to set the unit at a lowoutput speed when the scraper is starting from the Hunter back of themachine, to thereafter rapidly/accelerate the output speed of the unit,and to rapidlyrdecelerate the output speed of the unit asthe' scraperapproaches the front or rear of the machine.

l. Ina silk screen printing machine having a printing table, a scraper,a track guiding said scraper for movement back and forth across saidtable, a rotary shaft, means to turn said shaft in opposite directions,means governed. by the position of thescraper to reverse the rotation ofthe shaft when the scraper reaches the front of the machine and to stopthe shaft when the scraper reaches the rear of the machine, means tostart the scraper toward the front of the machine from the rear of themachine, a hydraulic speed-varying transmission unit for driving theshaft, a control member regulating the output speed of the unit, meansto drive the scraper from the unit, means governed by the position ofthe scraper and actuating the control member so as to set the unit at alow output speed when the scraper is starting from the front or back ofthe machine, to thereafter rapidly accelerate the output speed of theunit, and to rapidly decelerate the output speed of the unit as thescraper approaches the front or rear of the machine.

5. In a silk screen printing machine having a printing table, a scraper,a track guiding said scraper for movement back and forth across saidtable, a rotary shaft, means to turn said shaft in opposite directions,means governed by the position of the scraper to reverse the rotation ofthe shaft when the scraper reaches one end of the machine and to stopthe shaft when the scraper reaches the other end of the machine, meansto start the scraper toward the first named end of the machine from theother end of the machine, a hydraulic speed-varying transmission unitfor driving the shaft, a control member regulating the output speed ofthe unit, means to drive the scraper from the unit, means governed bythe position of the scraper and actuating the control member so as toset the unit at a low output speed when the scraper is starting fromeither end of the machine, to thereafter rapidly accelerate the outputspeed of the unit, and to rapidly decelerate the output speed of theunit as the scraper approaches either end of the machine.

6. In a silk screen printing machine having a printing table, a scraper,a track guiding said scraper for movement back and forth across thetable, an element, means to mount said element for reciprocation, apositive kinematic train interconnecting said scraper and said element,said train including a motion reducing mechanism whereby said elementduplicates in miniature the movement of the scraper, a reversibleelectric motor driving said scraper, switches actuated by said elementfor reversing the motor when the scraper reaches the front of themachine and stopping the motor when the scraper reaches the rear of themachine, a starting switch, and means for relatively adjusting thepositions of the first named switches and the element in the directionof movement of the scraper.

'7. In a silk screen printing machine having a printing table, ascraper, a track guiding said scraper for movement back and forth acrosssaid table, an element, means to mount said element for reciprocation, apositive kinematic train interconnecting said scraper and said element,said train including a motion reducing mechanism whereby said elementduplicates in miniature the movement of the scraper, a reversibleelectric motor, a hydraulic speed-varying transmission unit driven bythe electric motor, a control member regulating the output speed of theunit, means to drive the scraper from the unit, a control circuit forsaid electric motor, a starting switch, switches for governing theoperation of said motor, said last named switches and said controlmember being so disposed for actuation by said element that uponactuation of said starting switch said scraper will start "at slow speedfrom the rear of the machine, rapidly accelerate, subsequently rapidlydecelerate as it approaches the front of the machine, reverse at thefront of the machine, slowly start to the rear of the machine, rapidlyaccelerate, subse-- quently rapidly decelerate as it approaches the rearof the machine, and finally stop as it reaches the rear of the machine,and means for relatively adjusting the positions of the last namedswitches and the element in the direction of movement of the scraper.

8. In a'silk screen printing machine having a printing table, a scraper,a track guiding said scraper for movement back and forth across saidtable, a reversible electric motor, a positive kinematic traininterconnecting said scraper and said motor, an element, means to mountsaid element for reciprocation, a motion reducing mechanism driven by amember of said train and actuating said element whereby said elementduplicates in miniature the movement of the scraper, a control circuitfor said electric motor, a starting switch, and switches for governingthe direction of rotation of said motor, said last named switches beingactuated by said element in such manner that the scraper upon actuationof the starting switch will start from the rear of the machine, reverseat the front of the machine, and stop at the rear of the machine.

9. In a silk screen printing machine having a printing table, a scraper,a track guiding said scraper for movement back and forth across saidtable, a reversible electric motor, a positive kinematic traininterconnecting said scraper and said motor, a threaded element, athreaded shaft meshing with said threaded element, means to" actuated bysaid element in such manner that the scraper upon actuation of thestarting switch will start from the rear of the machine, reverse at thefront of the machine, and stop at the rear of the machine.

10. In a silk screen machine having a printing table, a scraper, a trackguiding said scraper for movement back and forth across said table, arotary shaft, a positive kinematic train interconnecting said shaft andscraper for driving said scraper, and a hydraulic speed-varyingtransmission unit in said train, said unit including a control memberfor regulating the output speed of the unit, said control member beingdisposed for actuation as the scraper approaches the end of its travelto rapidly deceleratethe scraper.

11. In a silk screen printing machine having a printing table, ascraper, a track guiding said scraper for movement back and forth acrosssaid table, a rotary shaft, a positive kinematic train interconnectingsaid shaft and scraper for driving the scraper, an element, means tomount said element for reciprocation, a positive kine-' matic traininterconnecting said scraper and said element, said last named trainincluding a motion reducing mechanism whereby said element duplicates inminiature the movement of the scraper, said first named train includinga hydraulic speed-varying transmission unit having a control memberregulating the output speed of the unit, said member being so disposedfor 13 actuation by said element that as the-scraper approaches an: endof the: machine the element will engage: the member: and rapidlyaccelerate j the output speed of the unit.

12.. In a silk screen printing machine. having a printing table, ascraper, a track guiding-said? scraper for movement each and forthacross said table, aneieine'nt, means'to mount said ole ing transmissionunit driven by the electric motor, a control member: regulating the"output speed or" the unit, means to drivc= the scraper from the unit, acontrol circuit for said electric motor, a starting. switch switches forgoverning the operation of said motor, and means adjustably mounted on.said element for actuating said last named switches and said controlmember so that upon actuation of said starting switch said scraper willstart at slow speed from the rear of the machine, rapidly accelerate,subseduently rapidly decclcrate as it approaches the front of themachine, reverse at the front the machine, slowly start to't'he'rea r ofthe'niachlne, rapidly accelerate, subsequently" rapidly decelerate as itapp-roaches the rear of the machine, and finally stop as it reaches therear of the machine.

13. In a sill: screen printin machine having a printing table, ascraper, a track guiding said scraper for movement back and forth acrosssaid table, an element, means to mount said element for reciprocation, apositive kinematic train interconnecting said scraper and said element,said train includinga motion reducing mechanism whereby said elementduplicates in miniature the movement of the scraper, a reversibleelectric motor, a hydraulic speed-varying transmission unit driven bythe electric motor, a control member regulating the output speed of theunit, means to drive the scraper from the unit, a control circuit forsaid electric motor, a starting switch, switches for governing theoperation of said motor, means adjustably mounted on said element foractuating the last named switches so that upon actuation of saidstarting switch said scraper will be driven from the rear to the frontof the machine, reverse, be driven to the rear of the machine and stop,and means adjustably mounted on said element for engaging the con- 1trol member tof'rapidly accelerate the output speed of the unit as thescraper starts from the front or rear of the machine and to rapidlydecelerate the output speed of the unit as the scraper approaches thefront 01- rear of the machine.

14. In a silk screen printing machine having a printing table, ascraper, a track guiding said scrap-er for movement forth across saidtable, an element, means to mount said element for reciprocation, apositive kinematic train interconnecting said scraper and said element,said til) 14 machine" and" at the? rear or the machine:

15.- In a silk screen printing machine havlng'a printing table, a;scraper, a track guiding said scraper for movementba'ck andzfurthacrosssaid table, an: element, means to mount said element for: reclprocatio'n;v a positive kinematic train iiitsrcomiecting said scraper andsaid element,-.sald train including a" motion reducing mechanism wherebysaid element-duplicates in miniature-the movement of thescraper, areversible electric motor, a hydraulic: speed-varying transmissionunit'drivenby the-electric motor, a control member regulating theoutputspeed of: the unit, xneans to drive the scrap'erfrom the unit,ineanstocontrol the' motor soas to startthe scrape'r'from-the rear-ofthe-machine, reverse it at the front of the machine and: stop it at therear of the machine; and means adjustably mounted on said elementforengaging the colitrolmember so as to rapidly accelerate the-output speedofth'e unit as the scraper starts from the front or rear of the machine:and to rapidlyidecelerate the-output speed or the: unit as the camperapproaches the front or rear'o'f the machine.

16; Ina silk-screen printing machine having a: printing. table, ascraper, a pair of tracks at opposite sides'of said scraper andextendingfrom the front to the' rear of the-machine, means supportingthe ends of saidscraper and: riding on said traclismeansto pivotallymount said tracks for oscillation about a common horizontal-- axis atthe rear of the machine, a pair of elongated flexible members, a rotarymember at the front and rear of each track about which the elongatedmembers are trained, means to connect said elongated members to theopposite ends of the scraper supporting means for driving the same, asecond rotary member at the rear of each track, said second rotarymembers being mounted for rotation about said common horizontal axis,means to rotate the first named rear rotary members from the last namedrotary members, and means to turn said last named rotary membersselectively in one direction or another, said last named means includinga countershaft, means operatively connecting said countershaft to saidlast named pair of rotary members, a threaded member on said shaft, athreaded element meshing with said threaded member so as to duplicate inminiature the movement of the scraper, a hydraulic speed-varyintransmission unit including a fluid motor and a variable delivery fluidpump, an electric motor driving said pump, a control member for saidpump, the regulation of which will change the output speed of the unit,switches for controlling the motor, and means movable by said elementfor operating said switches and said control member.

17. A combination as set forth in claim 16 wherein the switches includea stop switch and a reverse switch, and wherein the element includes afirst component adjustable mounted thereon for engaging the stop switchwhen the scraper reaches a selected point adjacent the rear of themachine and a second component adjustably mounted thereon for engagingthe reverse switch when the scraper reaches a selected point adjacentthe front of the machine.

18. A combination as set forth in claim 17 wherein the element includesa third component mounted therefor engaging the control member todccelerate the output speed of the unit when the scraper approaches theselected points adjacent the front or rear of the machine.

19. A combination as set forth in claim 16 wherein the switches includea stop switch and a reverse switch, wherein the element includes a firstcomponent adjustably mounted thereon for engaging the stop switch whenthe scraper reaches a selected point adjacent the rear of the machineand a second component adjustably mounted thereon for engaging thereverse switch when the scraper reaches a selected point adjacent thefront of the machine, and wherein the element includes a third componentmounted thereon for engaging the control member to decelerate the outputspeed of the unit when the scraper approaches the selected pointsadjacent the front or rear of the machine.

20. A combination as set forth in claim 16 wherein the switches includea stop switch and a reverse switch, and wherein the element constitutesayoke including two arms each of which ,adjustably supports a pair ofstuds, one of said adjustable studs on one of said arms being disposedto engage the stop switch when the scraper reaches a selected pointadjacent the rear of the machine, one of said adjustable studs on theother arm being disposed to engage the reverse switch when the scraperreaches a selected point adjacent the front of the machine, the otheradjustable studs on said arms being disposed to engage the controlmember just before the aforementioned studs engage the stop or reverseswitches so as to decelerate the output speed of the unit.

21. Ina silk screen printing machine having a printing table, a scraper,a track guiding said scraper for movement back and forth across saidtable, said track including two pairs of hollow tubes disposed atopposite ends of the scraper, each pair of tubes including an upper tubeand a lower tube, a sprocket rotatably mounted at the rear of each pairof tubes, a sprocket rotatably mounted at the front of each pair oftubes, means to reversibly rotate said rear sprockets, a pair of chainsone trained about the sprockets at each end of the scraper, the upperflight of each chain being disposed in an upper tube and the lowerflight of each chain being disposed in a lower tube, and meansconnecting one flight of each chain with the associated end of thescraper.

JOHN B. THOMAS.

References Cited. in the file of this patent UNITED STATES PATENTSNumber Name Date 2,039,909 Kern et al May 5, 1936 2,207,818 Perry et a1.July 16, 1940 2,267,596 Montague Dec. 23, 1941 2,355,930 Thorne Aug. 15,1944 2,571,685 DAutremont Oct. 16, 1951

